This invention relates generally to apparatus and a method for determining pressure differentials, such as the pressure differential between contiguous areas or zones where one is deliberately maintained at a higher or lower pressure than the other.
One typical example of an application where pressure differentials between contiguous zones must be maintained is in the textile field, and more particularly drying ovens for cloth. In apparatus of this type, a length of cloth is continuously passed through a generally enclosed zone or area having a plurality of burners disposed above and below the running length of cloth to generate heat that dries the cloth. In the process of drying the cloth, volatiles and toxic gases are generated which would be harmful to opertors or personnel in the surrounding area, and these volatiles and gases must be removed from the confines of the oven, usually by an exhaust blower. Because the drying oven, while being generally enclosed, must have some openings therein, such as openings that permit the running length of cloth to be introduced into and removed from the the oven, a danger exists that the aforesaid harmful gases may leak out of the oven and into the surrounding area, and, to avoid this danger, it is common practice to operate the exhaust blower at a high capacity that will insure that a decidedly negative pressure is maintained within the confines of the oven so that any air movement through the openings in the oven will always be inwardly from the outside surrounding area rather than vice versa. Moreover, because it is critical that the harmful gases not be permitted to escape from the oven, and because the pressure differential between the confines of the oven and the surrounding ambient zones will vary over a range, the exhaust blower is normally operated at a capacity that is substantially above that which is actually required to maintain the required negative pressure within the oven. While this arrangement generally solves the problems of harmful gases leaking out of the oven, it has practical drawbacks in that a large capacity exhaust blower is required and the operating costs of the blower are relatively high because of the high speed at which it is operated. In most instances the exhaust blower is operated at a constant speed that provides the aforesaid overcompensating capacity for air and gas removal, but it is known, in some instances, to regulate the speed of the blower in response to the moisture content of the air or the volume of air being removed from the oven.
On the other hand, it is sometimes necessary to maintain the pressure of one area or zone at a higher level that a contiguous area which is at atmospheric pressure to insure that any air flow will always be a direction toward the ambient area. For example, in hospital operating rooms, it is essential that antiseptic conditions be maintained within the confines of the operating room and that air in surrounding or adjacent rooms, which may contain germs or other contaminants, not be permitted to pass into the operating room through door openings, vents or other apertures in the walls. Accordingly, it is common practice to provide an inlet blower or other sources of pressurized air that constantly introduces pressurized air into the operting room to maintain it at a higher pressure than surrounding or continuous areas so that any air flow through the aforesaid wall openings or apertures will be in a direction from, rather than into, the operating room. Again, it is common practice to use an inlet blower that has a higher capacity than is actually needed, and to operate such blower at a generally constant high operating speed that is sufficient to overcompensate for the actual needs of maintaining a positive relative pressure within the operating room under all conditions, all of which increases the initial and operating costs of such installation.
In accordance with the present invention, an arrangement is provided for accurately determining the pressure differential between two areas, whereby such pressure differential can be maintained within close tolerances without requiring any significant overcompensation, and this arrangement is relatively simple and inexpensive, yet quite reliable.